Piezoelectric crystal structure



June 28, 1949. K K, GARRISON 2,474,241

PIEZOELECTRIC CRYSTAL STRUCTURE Filed June 29., 1945 Y afd. TM 1U:- u( /57 Y n V u ATTO R N EY Patented June 28, 1949 2,414,241 rmzoaLEcTmc caYsTAL STRUCTURE Kenton Kitch Garrison, East Orange, N. J., asslgnor to Federal Telephone and Radio Corporation, New York, N. Y.,

Delaware a.4 corporation of Application June 2s, 1945, serial No. 602,238 1o claim. (01.1'11--32'0 This invention relates to piezoelectric crystal structures and conductor mountings therefor designed for greater durability and to avoid certain objectionable conditions of mountings as heretofore used, particularly as related to fractures or breaking of electrical contact of` the electrode coatings in the region of the connecting support.

A prominent cause of failure and difficulty encountered with the present methods of crystal mountings results from the customary practice of directly connecting the supporting pins or wire conductors to the electrode Acoatings as for instance by solder connections. fracture and resulting -failure results particul'arly from the extreme thinness of the electrode coatings as employed. Electrodes of extreme thinness are employed by reason of their desired electrical characteristics and to avoid or reduce to a minimum interference such as damping or attenuation of the natural and determined crystalA vibrations. This direct connection of the supporting wires with the electrode is deficient y in mechanical or structural strength not only by reason of the thinness of the electrode material but is further weakened particularly with soldered connections by the alloying of the solder with the electrode metal reducing its adherence to the crystal surface. In certain structural A danger ofA forms, particularly in mountings operating `with contour mode of vibration of the crystal a degree of increased mechanical strength is customarily obtained by drilling of the crystal at the nodal point for thereception of the end of the mounting wire but there still remains a substantial degree of structural weakness at the union of the wire with the electrode such as to result in failure when subjected to shock or vibratory stresses.

In accordance with the present invention a more rugged and durable mounting supportfor resonance elements having electrodes of the desired minimum thickness is provided by initially applying to the surface of the crystal, a localized small area deposit or subiayer of metal, positioned at the nodal area of the crystal and point of support. This localized metal layer, desirably of silver, is provided for mechanical reinforcement and is of a metal or alloy strongly adherent to the crystal surface. The electrode metal is thereafter applied to the crystal surface with the material thereof extended onto and over the localized silver deposit. The thus reinforced supporting or connecting portion is then drilled for the reception of the end of the supporting pin or conducting lead.

The localized subiayer is of a thickness which in the instance of certain mountings will proonto the crystal surface. The electrode material is then adherently applied thereover. A bore is then formed by drilling through the electrode and into the reinforcing metal for the reception of the supporting pin or conducting lead for sup- I porting of the crystal in like manner and desirably with a supporting pin formed to effect a clamping engagement with the electrode by pressure applied between the supporting pin and crystal.

The described and other features and advantages of the present invention will be more fully `understood by reference to the accompanying drawings wherein like characters are applied to the corresponding parts in the several views.

In the drawings:

resonator unit assembly showing the crystal and mounting unit in elevation- Fig. 2 is a vertical section through the center of a crystal element of the piny mounted type y and showing the supporting pins inelevation;

Fig. 3 isa similar view illustrating the features of the invention as embodied in the crystal structure. wherein the crystal elementv is drilled in one face thereof; y

Fig. 4 is a central sectional view of the crystal structure employing the nodal area reinforcement of the invention adapted for spring contact support;

Fig. 5 is a further modication ofthe type of mounting for directly securing upon the end of conductor leads.

In the preferred embodiment of the .features of the present invention as here illustrated, the resonator or crystal element is shown enclosed within and supported by a holder of a standard type. In this structural embodiment the crystal is indicated at I positioned within an opening 2 Fig. 1 is a vertical sectional view of a typical I upper end with a reduced diameter contact ahoulderportion il engaslngtheimdersurfaoe ofthecrystal. Theuppersupportingandconaperture and resiliently engaged by a spring Il of i'lat metal having its right hand end portion underlying the terminal l for electrical connectionandsecuredatitsoppositeendbythescrew i1 threaded to the holder. The arrangement insofar as described accordingly provides for supporting of the crystal .with a rest bearing upon the lower pin Il and with pressure engagement of the upper pin il therewith and with the c ircuit closed to the respective terminal pins il and l'l through the crystal elements by the supporting engagement with the electrodes thereof.

In accordance with the invention the resonator or crystal element is of the usual rectangular plate formation provided on its opposite faces with electrode layers or coatings IIand il and is likewise provided at its central or nodal portion with a y localized sublayer of reinforcing metal 2l adherently applied to the crystal preparatory to the applying of the electrode thereon and over which the electrode metal is adherently applied in a thin layer as by spraying by the well known Schoop method.

This sublayer may be applied as a silver paste such as that known as Hanovia 122 A composed of free silver. lead borate and a solvent which uponbaklnghasgoodadherencetothecrystal surface.

This small area sublayer Il may have a thickness of from .0002" up to .020" depending on the mounting method. and is heat treated or baked at from 500 to 550 C. with slow cooling. This thickness is not critical and may be varied.

Thereafter the electrode metal is asshown ap.

toflligamodiwhereinthecrystalelementis drilledinonemrfacetoprovideabore-Minthe area for mounting attachthhinstance In Plas. 4 and 5 other suitable modifications 'embodying certain features of the invention are disclosed as incorporated in other known types of mounting. In that of Fig. 4 the mounting of the crystal is by means of opposed resilient spring contacts 2i in opposed relation having pressure engagement at the central nodal point of the crystal element by means of the contact beads Il. Inthisinstancethelocalisedsublayersl'l are applied to underlie the electrode material for wear reinforcement as in connection with the lower pin support of the preceding figures. In the disclosure of Fig. 5 the sublayer reinforcing metal indicated at 2l and underlying the electrode material II and il is drilled in corresponding manner to the upper mounting of Pig. 2 for the reception of the end of supporting and conducting wires 2l in resiliently opposed relation and alignment as employed in theA customary lead or wire supported crystal mountings as used for the mounting of crystals of. very small aises.

'Ihe mounting of the crystal with elimination of rigid union with the electrode material, results in increased stability of operation over long periodsofuse. Inthisconnectionandaswill be appreciated, the effects of wear incident to vibrations or shock. will have no appreciable effect upon the conditions of support or upon the maintenance of good electrical contact. In the embodiment of the invention as disclosed in Figs.

plied to the crystal surface to overlie the circular reinforcement and in the mounting arrangement as disclosed in Fig. 2 the upper sublayer 2l is drilled through the electrode material providing a small bore for the reception of a pin or wire contact extension 2| integral and concentric with the reduced shoulder il of the upper pin Il. This bore desirably does not extend through the layer 2l which provides that there shall be butt end electrical contact if pin engagement occurs at the bottom of the bore and if such engagement is absent. similar butt end engagement will occur under the spring mounting pressure between the end surface of the shoulder il and the elec- 2 and 5 there ispresented the advantage of eliminating losses due to chipping of the crystal incident to drilling into the crystal itself.

While there is shown and described desirable embodiments of the features of the invention, it willbeunderstoodthatvariedmodiiicationsmay be made therein without departing from the scope thereof as donned in the appended claims.

What is claimed is:

l. A piezoelectric device comprising a crystal. said crystal having a localised area metal deposit adheringly applied at a nodal region, electrode coatings adheringly applied over the crystal faces and over the metal deposit and said deposit beingdrilledtoprovideaboreforthereceptionof a mounting pin.

2. A piezoelectric device comprising a crystal, said crystal having a localised area metal deposit adheringly applied to opposite faces of the crystalatiisnodalregion, electrodecoatingsadlheringly applied over the crystal faces and over the metal deposits and at least one of said depositsbelngdriiledtoprovideaborefortherecaption of a pin.

ception of a mounting pin and a mounting pin slidably tted within the bore.

4. A piezoelectric device comprising a crystal, said crystal having a localized area metal deposit adheringly applied at its nodal region, electrode coatings, adheringly applied over the crystal faces and over the metal deposit and said deposit being drilled to provide a bore for the reception of a mounting pin in position of nonengagement with the crystal and a mounting pin slidably fitted within the bore.

5. A resonator element of the character described comprising a crystal element having localized area metal deposits on its opposite faces adheringly applied at its nodal region, electrode coatings adheringly applied to the crystal faces and extended over the metal deposit and said element being formed with at least one bore in al deposit adapted to receive a mounting pin slidably ntted thereto and resiliently engaging supporting means for the crystal including a pin slidable within the bore.

6. A resonator element of the character described comprising a crystal element having localized area metal deposits on its opposite faces adheringly applied at its nodal region, electrode coatings adheringly applied to the crystal faces and extended over the metal deposits and adapted for resiliently supporting the crystal with slidable engagement with the denolts.

'1. A resonator element of the character described comprising a crystal element having localized area metal deposits on its opposite faces adheringly applied at its nodal region, electrode coatings adheringly applied to the crystal faces and extended over the metal deposit, said crystal being formed with at least one bore in a face thereof within which the deposit metal extends and having a bore formed therein for the reception of a supporting pin and a supporting pin slidably fitted to the bore.

8. A resonator element of the character described comprising a crystal element having localized area metal deposits on its opposite faces adheringly applied at its nodal region, electrode coatings adheringly applied to the crystal faces and extended over the metal deposit, said crystal being formed with at least one bore in a face thereof within which the deposit metal extends and having a bore formed therein for the reception of a supporting pin and a supporting pin slidably fitted to the bore and formed for shoulder engagement with the electrode.

9. A resonator element of the character described comprising a crystal element having localized area metal deposits on its opposite faces adheringly applied at its nodal region, electrode coatings adheringly applied to the crystal faces and extended over the metal deposit and said element being formed with aligned bores in the deposits adapted to receive mounting pins sldably fitted thereto.

i0. A piezoelectric device comprising a crystal, a localized area metal contact piece secured to said crystal, an electrode coating covering said contact piece and the adjacent surface of said crystal, said contact piece being drilled to provide a bore for the reception of a. mounting pin.

KENTON KITCH GARRISON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,366,954 Brooks Jan. 9, 1945 2,371,613 Fair Mar. 20, 1945 

